First discoveries? Alan Barr University of Oxford

13 April '07Alan Barr, Cosener's House2 Disclaimers I haven’t done a year of analysis of 14 TeV data  Few of us have I haven’t done a “new physics” search at the Tevatron LEP, HERA or SPPS Acutely aware that many others have! Few have claimed “new” physics My best credentials… “I haven’t made a claim I’d seen new physics which later turned out to be false” My best credentials… “I haven’t made a claim I’d seen new physics which later turned out to be false”

13 April '07Alan Barr, Cosener's House3 Let’s get it out of the way… Stuck Magnetic Monopoles After sorting out cabling map …

13 April '07Alan Barr, Cosener's House4 Cross-sections etc What can we find with 100 pb -1 to 1 fb -1 ? –Reasonable cross-section –Low backgrounds –Easily reconstructed –Limited detector understanding? Some things should “stick out like a sore thumb” Others need more careful analysis Much relies on topics already covered Lower backgrounds Higher backgrounds “Rediscover” “Discover” ZZ WW

13 April '07Alan Barr, Cosener's House5 Taught to “rediscover” Z’s W’s and tops are not just used for “detector calibration” –MC validation –Build confidence in analysis methods Need to be measured as backgrounds to new physics Getting started… can see top with “no” b-tagging Tagging clearly helps though! no b-tag b-tag + W mass window Reconstructed top mass/GeV

13 April '07Alan Barr, Cosener's House6 After bosons … di-bosons Again – an important background for various studies: –Higgs -> VV –Vector boson rescattering –Slepton/gaguino –SUSY trilepton searches –… Then Tribosons? c.f. Campbell

13 April '07Alan Barr, Cosener's House7 What needs to be working? Resonances Continuum signals Missing energy Complex topologies Resonances Continuum signals Missing energy Complex topologies Harder? All components calibrated All backgrounds understood Some components calibrated Some backgrounds understood A lot of the well-motivated stuff lies towards the bottom of this list: much of SUSY, complex Higgs decays, … How quickly can we get there? C.f. Chris Hill Good news: If you are aware of the problem it’s ten times easier… Wire bonds Cosmic commission early … Bad news: We’ll most likely have a whole different stack of new problems Bad news: We’ll most likely have a whole different stack of new problems “Missing energy takes (took) 3 years” “Leptons first, Jets later” Involate? “Missing energy takes (took) 3 years” “Leptons first, Jets later” Involate?

13 April '07Alan Barr, Cosener's House8 Rapidly exceed Tevatron reach for new gauge bosons “Sore thumb” territory Need e.g. ECAL cross-calibration & scale Events triggered & read out (trigger efficiency for high energy leptons?) 10 fb -1

13 April '07Alan Barr, Cosener's House9 Continuum distributions: dijets Decreasing scale of new contact interaction Strategy for poorly known systematics? Normalise in “outer” rapidity region Measure in “inner” rapidity Try to factor out e.g. energy scale Strategy for poorly known systematics? Normalise in “outer” rapidity region Measure in “inner” rapidity Try to factor out e.g. energy scale 1fb -1

13 April '07Alan Barr, Cosener's House10 R P conserving SUSY makes Jets, Leptons and missing transverse momentum –Cascade decays –Complicated events –Difficult background estimation SUSY and so on

13 April '07Alan Barr, Cosener's House11 Those exclusion plots Statistical-only coverage if background already known! Often assume good knowledge of very complex final states E.g. “6 jets + 1 lepton + missing energy > 200 GeV” + …

13 April '07Alan Barr, Cosener's House12 First attack missing E T Started already with MC studies – e.g. punch-through, cracks etc.

13 April '07Alan Barr, Cosener's House13 Typical requirements Tracker, ECAL, HCAL, muons, FCAL all “needed” CMS physics TDR Cross-calibration of HCAL clearly important Missing energy in there… of course

13 April '07Alan Barr, Cosener's House14 Background normalisation… Getting backgrounds wrong makes a big difference –Design analysis to reduce them Measure them in situ –Independent extraction of different backgrounds needed –Preferably unbiased by any new physics CMS

13 April '07Alan Barr, Cosener's House15 Backgrounds from data… Example: SUSY BG –Missing energy + jets from Z 0 to neutrinos –Measure in Z -> μμ –Use for Z -> Good match –Useful technique Statistics limited –Go on to use W -> μ to improve   Measure in Z -> μμ Use in Z -> νν R: Z  B: Estimated R: Z  B: Estimated

13 April '07Alan Barr, Cosener's House16 Measuring QCD jets backgrounds to SUSY? Control sample has large missing ET close to one jet Assume this jet has fluctuated to cause MET Use this to measure tails of the jet resolution Method describes the QCD BG well in the tail region which it has been designed for Assume jets are independent Apply the resolution function to all jets in sample of events with initially small missing ET  Estimate of QCD BG

13 April '07Alan Barr, Cosener's House17 Keep it simple? Small N jets + E T Select a small number of high P T jets –Large signal cross-section –Large control statistics –Relatively well known SM backgrounds Relatively “model independent” –Does not rely on leptonic cascades –Does not rely on hadronic cascades Use kinematics rather than “busyness of event” to pick out SUSY SIGNAL topology BACKGROUND topology (QCD)

13 April '07Alan Barr, Cosener's House18 Jets-only measurement 1 fb -1 ATLAS Geant4 Keeping it simple –>=2 jets –E T (J 1,2 ) > 150 GeV; | η 1,2 | < 2.5 –Plot M T2 –N.B. M T2 → 0 if: E T → 0 E T parallel to either jet Jet E T → 0 Designed for mass measurements Useful for searches? Violates the Tevatron “leptons first rule” – problem?

13 April '07Alan Barr, Cosener's House19 Electroweak symmetry breaking? Not the easiest thing to attack quickly –Small couplings to most fermions –Large backgrounds and/or difficult final states b-tagging/taus/ missing energy –But clearly a high physics priority CMS Higgs-> γγ with 1 fb -1 Signal scaled by x10 !

13 April '07Alan Barr, Cosener's House20 Any hope of a rapid Standard Model Higgs? “Under the streetlight” is near 160 GeV with H->WW->lνl ν Is this the Higgs we’re looking for? ATLAS Low mass harder CMS H->γγ “simpler” than ttH ; H-> bb

13 April '07Alan Barr, Cosener's House21 H-> WW -> l ν l ν Best chance for early discovery No mass peak Signal at small Δφ (spin correlations) Control samples from high m ll and large Δφ CMS

13 April '07Alan Barr, Cosener's House22 C. Lazzeroni, IoP half day meeting, UCL, Oct ‘06 First discoveries at LHC may not come from General Purpose Detectors… …if flavour or CP violating

13 April '07Alan Barr, Cosener's House23 Bump-hunting at LHCb…

Diversion

13 April '07Alan Barr, Cosener's House25 Fun: Revisit the 2003 ATLAS blind data challenge July 2003 –450 pb -1 simulated data (GEANT) –Single lepton trigger –Collaboration told “something in the data” Interesting why? –Which analysis strategies do we really employ? –Test our own confidence in what we see –Learn from mistakes! Much media interest in random numbers! No detector effects, halo, Miscalibration … No detector effects, halo, Miscalibration …

13 April '07Alan Barr, Cosener's House26 Checking the backgrounds Does the MC match the “data”? Is the detector calibrated? Do we have a reasonable background estimate? m ee m μμ Able to find which parts of our simulation don’t match the “data”: Pink part is double counted in simulation

13 April '07Alan Barr, Cosener's House27 Confidence in our findings?

13 April '07Alan Barr, Cosener's House28 SUSY? Excess of high mass stuff? SUSY-like signatures… Missing transverse momentum Leading jet E T In this case discrepancy was due to bias from generator P T distribution: low P T top quark generation lost in “Data”

13 April '07Alan Barr, Cosener's House29 “First discoveries” “Easy” to reconstruct Bumps on falling backgrounds! m ee m μμ

13 April '07Alan Barr, Cosener's House30 Charged resonance Excess at large transverse mass is not hard to pick out m T (electron) m T (muon)

13 April '07Alan Barr, Cosener's House31 Results: No one had confidence enough to claim non-PDG Top mass Some (far from complete) background validation achieved Resonances were obvious to all Properties of resonances could start to be uncovered No one looked for Higgs No one had confidence enough to claim non-PDG Top mass Some (far from complete) background validation achieved Resonances were obvious to all Properties of resonances could start to be uncovered No one looked for Higgs

Back to reality… What would make us smile?

13 April '07Alan Barr, Cosener's House33 Assume we have MSSM-like SUSY with m(squark)~m(gluino)~600 GeV See excesses in “typical” distributions: –Missing transverse energy –Scalar sum E T –Dilepton spectrum (below) with edge Assume we have MSSM-like SUSY with m(squark)~m(gluino)~600 GeV See excesses in “typical” distributions: –Missing transverse energy –Scalar sum E T –Dilepton spectrum (below) with edge

13 April '07Alan Barr, Cosener's House34 What might we have found out? Can say some things: –Undetected particles produced missing energy –Some particles mass ~ 600 GeV, couplings similar to QCD “Effective mass” & cross-section –Some of the particles are coloured jets –Some of the particles are Majorana excess of like-sign lepton pairs –Lepton flavour ~ conserved in first two generations e vs mu numbers –Possibly Yukawa-like couplings excess of third generation –Some particles contain lepton quantum numbers opposite sign, same family dileptons –… Can say some things: –Undetected particles produced missing energy –Some particles mass ~ 600 GeV, couplings similar to QCD “Effective mass” & cross-section –Some of the particles are coloured jets –Some of the particles are Majorana excess of like-sign lepton pairs –Lepton flavour ~ conserved in first two generations e vs mu numbers –Possibly Yukawa-like couplings excess of third generation –Some particles contain lepton quantum numbers opposite sign, same family dileptons –… Slide based on Giacomo’s There will be lots more to do after this!

13 April '07Alan Barr, Cosener's House35 Conclusions? We don’t know what we will find –Value of prejudices rapidly decreases with data! Sure to be hard work –It already has been for some time! Terra Incognita in very many ways –Human as well as technical aspects Opportunities abound “I find all this stuff simply fascinating!” “Jim of the Hog’s Bosun” (My retired neighbour) “I find all this stuff simply fascinating!” “Jim of the Hog’s Bosun” (My retired neighbour)

13 April '07Alan Barr, Cosener's House36 Fin

13 April '07Alan Barr, Cosener's House37 Check for weirdos Electron-muon invariant mass Well matched – gave some degree of confidence in “new physics” invariant masses

13 April '07Alan Barr, Cosener's House38 W contribution to no-lepton BG Use visible leptons from W’s to estimate background to no-lepton SUSY search Oe, Okawa, Asai

13 April '07Alan Barr, Cosener's House39 Normalising alone not necessarily good enough Distributions are biased by lepton selection  Distributions are biased by lepton selection 

13 April '07Alan Barr, Cosener's House40 Need to probe deeper…

13 April '07Alan Barr, Cosener's House41 Then possible to get it right… Similar story for other backgrounds – control needs careful selection

13 April '07Alan Barr, Cosener's House42 Gauge Mediated SUSY Breaking Signature depends on Next to Lightest SUSY Particle (NLSP) lifetime Interesting cases: –Non-pointing photons –Long lived staus Extraction of masses possible from full event reconstruction More detailed studies in progress by both detectors

13 April '07Alan Barr, Cosener's House43 GMSB: non-pointing  event  cluster (1 st layer – IP)  rec poiting (egamma obj) G~ 01010101~

13 April '07Alan Barr, Cosener's House44 R-hadrons Motivated by e.g. “split SUSY” –Heavy scalars –Gluino decay through heavy virtual squark very suppressed –R-parity conserved –Gluinos long-lived Lots of interesting nuclear physics in interactions –Charge flipping, mass degeneracy, … Importance here is that signal is very different from standard SUSY

13 April '07Alan Barr, Cosener's House45 R-hadrons in detectors Signatures: 1.High energy tracks (charged hadrons) 2.High ionisation in tracker (slow, charged) 3.Characteristic energy deposition in calorimeters 4.Large time-of-flight (muon chambers) 5.Charge may flip Trigger: 1.Calorimeter: etsum or etmiss 2.Time-of-flight in muon system –Overall high selection efficiency –Reach up to mass of 1.8 TeV at 30 fb -1 GEANT simulation of pair of R-hadrons (gluino pair production)